The present invention relates to a seat belt retractor for preventing pulling-out of a webbing, which is wound on a reel shaft when the webbing is suddenly pulled out or when sudden acceleration occurs.
Conventionally, a seat belt unit is mounted on a seat in an automobile for protecting an occupant in an emergency such as vehicle collision. A webbing in such seat belt unit is wound on a reel shaft of an emergency locking type retractor unit, which is mounted on a reinforced member of the vehicle. When an occupant puts the webbing on, the webbing can be freely pulled out from the retractor unit in normal case so that the occupant is not restrained from moving. On the other hand, when an emergency such as vehicle collision occurs, reel shaft locking means of the retractor unit is operated by detecting impact force or sudden acceleration, and rotation of the reel shaft, which takes up the webbing, is locked. By this locking of the rotation of the reel shaft, the webbing restrains and protects the occupant by hindering him or her from sudden moving.
The reel shaft locking means can reliably stop the rotation of the reel shaft itself, which takes up the webbing. In some cases, however, the webbing taken up in excess on the reel shaft is pulled out by tightening phenomenon even when the rotation of the reel shaft is stopped. To prevent the pulling-out of the webbing by the tightening, a seat belt retractor as shown in FIG. 2 and FIG. 3 has been proposed.
As shown in FIG. 2 and FIG. 3, the seat belt retractor 1 comprises a cylindrical reel shaft 4 rotatably mounted on a frame 2 and for taking up a webbing 3, a pendulum 5 mounted on the frame 2 and tilted when an impact force higher than a predetermined value is applied, a ratchet coaxially fixed on the reel shaft 4 for taking up the webbing 3, a link 7 operated by tilting of the pendulum 5, thereby engaging a pawl 7a with tooth 6a of the ratchet 6 and moved upward by rotating force of the ratchet 6, and a stopper member 9 mounted on the frame 2 and moved by upward movement of the link 7 and squeezing the webbing 3 between itself and a receiving member 8 fixed on the frame 2. A webbing squeezing mechanism is formed by the link 7, the receiving member 8 and the stopper member 9.
In the seat belt retractor 1 with such arrangement, the pendulum 5 is tilted in an emergency, and the pawl 7a of the link 7 is moved to a position for engaging with the tooth 6a of the ratchet 6. As the webbing 3 is pulled out, the reel shaft 4 and the ratchet 6 are rotated. By the rotation of the ratchet 6, the tooth 6a of the ratchet 6 is engaged with the pawl 7a of the link 7, and the link is moved upward. By the upward movement of the link 7, the stopper member 9 is rotated upward, and the webbing 3 is squeezed between the stopper member 9 and the receiving member 8. As the result, pulling out of the webbing 3 due to tightening can be prevented.
However, the webbing squeezing mechanism in a conventional type seat belt retractor 1 comprises a link 7, a receiving member 8 and a stopper member 9, and the rotating force of the ratchet 6 is transmitted to the stopper member 9 through the link 7. As the result, the mechanism is very complicated, and many component parts are required. This makes the seat belt retractor 1 more complicated in structure and larger in size.
After performing various tests on the tightening phenomenon of the webbing 3, it has been found that the tightening is caused by:
(1) slipping between the webbing 3 and outer peripheral surface of the reel shaft 4, and slipping between the coils, and PA1 (2) elongation of the webbing 3 itself.
Above all, (1) is the major cause of the tightening phenomenon.
Describing the above conventional type seat belt retractor 1 in detail, cross-section of the reel shaft 4 is in circular or spiral form. When the webbing 3 is taken up on the reel shaft 4, the webbing 3 is wound on outer peripheral surface of the reel shaft 4 and over the entire outer peripheral surface of the webbing 3 of the previous turn by approximately uniform compressive force. Thus, the compressive force applied on the webbing 3 is almost uniformly dispersed on the entire surface of the webbing 3, and it is relatively low. As the result, it is very difficult to have high friction force between the webbing 3 and outer peripheral surface of the reel shaft 4, and between the webbing coils.
Therefore, the major cause for generating the above tightening, i.e. the cause (1) above, is present on the conventional type seat belt retractor 1. Thus, in the conventional type seat belt retractor 1, the pulling-out of the webbing 3 by the cause (1) is prevented by squeezing of the webbing 3 by means of the webbing squeezing mechanism. Specifically, in the conventional type seat belt retractor 1, the webbing squeezing mechanism for preventing the webbing 3 from pulling out due to tightening is essential and indispensable, while the above webbing squeezing mechanism causes problems as already described.